Various types of color display technologies are known in the art. For example, there are CRT display systems, LCD systems, and projection display systems. In front projection displays, the projected images are viewed from a reflective viewing screen. In rear projection displays, the projected images are viewed through a transmissive viewing screen.
To produce color images, existing display devices use three primary colors, typically, red green and blue, collectively referred to as RGB. In simultaneous projection display systems, the three primary color components of the image are modulated and displayed simultaneously using one or more Spatial Light Modulators (SLMs).
FIG. 1 schematically illustrates an optical configuration 100 of a RGB display device implementing three transmissive Liquid Crystal Display (LCD) panels to produce a color image. The light from a lamp 102 passes through a combination 104 of IR/UV cutoff filters, an integrator and polarizing conversion system, and a lens, to obtain an s-polarized white light beam. This beam is split into three color channels using two dichroic mirrors. A first dichroic mirror 106 reflects the red part, while passing the blue and green parts of the spectrum; and a second dichroic mirror 108 separates the green part from the blue part. Each of the colored beams may pass through an additional color filter to obtain a better definition of its color. The three colored beams are then imaged on three LC spatial light modulators, 119, 120, and 121, respectively, to create three primary images, respectively. The three modulated primary images are then combined using a standard “X cube” 110. The combined images are then projected on a screen by a projection lens 112.
Since cube 110 is designed to reflect the red and blue s-polarization beams, and to transmit the green p-polarization beam; and since the illumination path carries s-polarized light, the polarization of the green beam has to be rotated to p-polarization before X-cube 110. This is done by inserting a polarization rotating plate after modulator 120.